1. Field of the Invention
The present invention relates to an impedance measurement technique.
2. Description of the Related Art
In order to measure an impedance component such as resistance, capacitance, inductance, or a value accompanying such an impedance component, various kinds of measurement methods are employed, examples of which include the bridge method, the resonance method, the I-V method, the RF I-V method, the network analysis method, and the automatic balancing bridge method. In many cases, commercially available network analyzers and LCR meters employ the network analyzing method or otherwise the automatic balancing bridge method. Such an arrangement provides high-precision measurement. However, as tradeoff problems, such a measurement method leads to a very high cost, and requires a long measurement time.
FIG. 1 is a diagram showing the principle of the resonance method. FIG. 1 shows an example of measurement of the impedance Z of a circuit comprising an inductance Lx and a resistance Rx connected in series. In a case in which the impedance Z to be measured functions as an inductive impedance, a variable capacitor C for tuning is arranged in series with the impedance Z, thereby forming an RLC series resonance circuit. With such an arrangement, an AC measurement signal is applied by means of a signal generator SG between both terminals of the series resonance circuit thus formed. In this state, at least one of the capacitance of the variable capacitor and the frequency of the measurement signal is adjusted so as to tune the circuit to a resonance state.
With such a resonance method, the value of the inductance Lx can be measured based on the capacitance value of the variable capacitor C and the frequency in the resonance state. Furthermore, based on the voltage across both ends of the variable capacitor, the Q value of the circuit, and thus the resistance Rx, can be measured.